1. Field of the Invention
The disclosed invention generally relates to bonding thin wire leads in microelectronic circuits, and is particularly directed to a bonding tool and wire clamp assembly for wire bonding apparatus and to a method for wire handling.
2. Background Art
In the manufacture of microelectronic circuit packages, certain electrical connections are made with extremely thin gold or aluminum wires. For example, connections between a semiconductor integrated circuit chip and the package leads are typically made with such thin wires. As another example, active elements in semiconductor hybrid circuits may be interconnected with extremely thin wire.
The attachment of interconnecting thin wires is typically accomplished with wire bonding machines which supply wire and make the connections of the opposite ends of the wire leads. Generally, a wire bonding machine includes a bonding head which can move vertically, horizontally and rotatably about a vertical axis. A transducer (e.g., an ultrasonic transducer) is pivotally mounted to the bonding head so as to pivot about a horizontal axis, preferably at the center of gravity of the transducer and its mount. The transducer includes an arm portion with a bonding tool at its end. The bonding tool is raised and lowered relative to the workpiece by vertical movement of the bonding head.
The increased complexity and reduction in size of integrated circuits has resulted in smaller areas available for bonding pads. As a result, wedge-wedge bonding is becoming more significant than the commonly used ball-wedge bonding.
Presently known bonding tools for wedge-wedge bonding include bonding tools which incorporate angle feeding of the wire under the foot of the bonding tool. While such angular wire feed may provide excellent results, small clearances near package walls posed impossible tasks for angled wire feed with normal forward wire bonding where the first bond is made to the integrated circuit chip and the second bond is made to the package. Reverse bonding (back bonding) has been suggested as a solution, but making second bonds on integrated circuit pads creates other problems. For example, the lay of the wire is lower near the second bond, thereby increasing the possibility of unwanted shorting contacts. Also, second bonds cannot be located as accurately as first bonds. Typically, the bonding areas on integrated circuits are smaller than the bonding areas on packaging elements.
Other presently known bonding tools include capillaries with vertical wire feed and would provide appropriate clearance at package walls. However, with such vertical wire feed bonding tools, wire control is difficult since the distance between the wire clamp and the bonding foot is typically quite substantial, on the order of several hundred times the wire diameter. Twists, kinks and bends may be readily formed between the wire clamp and the bonding tool foot.